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nLab > Latest Changes: co-Yoneda lemma

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    • CommentRowNumber1.
    • CommentAuthorUrs
    • CommentTimeJun 2nd 2016

    At co-Yoneda lemma I have tried to harmonize the notation and polish the formatting a little. For instance, earlier the statement had been in terms of VV-enrichment, but then the proof was stated in terms of SetSet-enrichment, I have harmonized that.

    Then I added as an Example an elementary proof of the co-Yoneda lemma in SetSet in terms of inspecting the defining coequalizer as a set of equivalence classes of pairs.

    • CommentRowNumber2.
    • CommentAuthormattecapu
    • CommentTimeNov 2nd 2023

    mention density formula and ninja Yoneda

    diff, v24, current

    • CommentRowNumber3.
    • CommentAuthorUrs
    • CommentTimeNov 2nd 2023

    For what it’s worth, this claim looks incorrect:

    In this MO answer, Tom Leinster referred to the co-Yoneda lemma as ninja Yoneda lemma

    On the contrary, he says that “ninja category theorists” would call it just the plain “Yoneda lemma”.

    I think jokes enshrined in mathematical terminology get old quickly and then stay old forever. I vote for not promoting this.

    • CommentRowNumber4.
    • CommentAuthorvarkor
    • CommentTimeNov 2nd 2023

    I think jokes enshrined in mathematical terminology get old quickly and then stay old forever. I vote for not promoting this.

    I completely agree.

    • CommentRowNumber5.
    • CommentAuthorUrs
    • CommentTimeNov 24th 2023

    I took the liberty of deleting the “ninja”-section.

    Because, first, it’s claim that “Tom Leinster referred to the co-Yoneda lemma as ninja Yoneda lemma” was just false, and second its mathematical content was a direct repetition of the material in this entry.

    (There may be room to state this material more clearly/concisely, but repeating it as if it were a different statement is confusing.)

    diff, v26, current

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